1. Field of the Invention
The invention relates to the upgrading of weak soil areas having low bearing strength, such as alluvial soil or hydraulic fill areas, into compacted soil having high bearing strength.
2. Description of the Prior Art
A prior art soil compaction method has been proposed which uses a vibratory driver to force an open-bottom-ended tube into the ground whereby to compact soil within and outside of the tube, the tube subsequently being vibratorily extracted to enhance compaction. This method has found commercial application as described in an article by Millard et al., "Graving Dock for 300,000 Ton Ships," which appeared in the June 1971 issue of "Civil Engineering - ASCE," and also in an article by Donnelly entitled "River Yields to Below-Sea-Level Dock Construction" which appeared in the March 1971 issue of "Construction Methods and Equipment."
Earlier prior art techniques for soil compaction entailed the usage of sheeps foot rollers or a tamping action employing air hammers or the like. In these techniques, successive layers of the soil were individually successively treated to achieve a measure of compaction. These methods obviously were primarily applicable where a filling of soil was taking place so that successive layers of soil were accessible, i.e., these methods were not generally applicable to in situ alluvial soils or the like or to hydraulic fill.
Other methods of soil compaction in which sand columns or crushed stone columns were formed are described in an article entitled "New Sand Drain Technique Strengthens Weak Soils" which appeared in the April 1971 issue of "Roads and Streets," and in an article entitled "In-Place Treatment of Foundation Soils" which appeared in the January 1970 issue of the "Journal of the Soil Mechanics and Foundations Division, ASCE."